THIS invention relates to a method of treating a plant or crop and to a treatment installation for the treatment of plants or crops.
Active chlorine in the form of hypochlorous acid, produced by the inorganic and organic hypochlorites and sources of active chlorine such as chlorine gas, sodium hypochlorite bleach (NaOCl), calcium hypochlorite Ca(OCl)2 and the organic chlorinated isocyanurates (trichloro- and sodium dichloro S-triazines) have been used for over 50 years for post-harvest protection of produce and for the control of fungi and bacteria to prevent rot-spoilage. However, due to phytotoxicity, these compounds have generally not been applied in the spraying of live crops for the control of fungal and bacterial diseases by exploitation of the bactericidal and fungicidal properties of the active ingredient hypochlorous acid. In particular, calcium hypochlorite has generally not been used because of vagaries in dissolution and difficulty in the control of concentration. Calcium hypochlorite of the 65-70% product type contains sodium chloride, which is phytotoxic at the high concentration levels required to produce hypochlorous acid for the killing of fungi and bacteria.
This invention provides a method of using calcium hypochlorite in millimolar quantities for the treatment of plants or crops in the field. In accordance with the invention, the plant cell surface of the crop is exposed to millimolar quantities of non-ionized, covalently bonded, hypochlorous acid, calcium and hydroxide ions in an ideal physiologically balanced form. Because hypochlorous acid is unstable, dissipates and is readily destroyed by light, the method of the invention incorporates the use of a wetting agent to ensure complete contact between plant cell wall and active hypochlorous acid, calcium and hydroxide ions. The result of the treatment is epidermal fortification of the plant cell wall. The invention thus differs from known methods in which microbial organisms are killed by hypochlorous acid.
The invention thus provides a method of treating a plant or crop which includes the step of exposing the plant or crop to an aqueous medium which contains treatment agents which include at least one wetting agent, calcium cations and hypochlorous acid representing therefore a technique of non-exploitation or exclusion of the bactericidal and fungicidal properties of hypochlorous acid, the concentration of the calcium hypochlorite and the calcium being approximately 17.38-34.76 ppm and 7.6-15.2 ppm respectively.
To the best of the Applicant""s knowledge, concentrations at this level, which are similar to the physiological concentration of calcium in plants, can only be dispensed in accordance with the method and apparatus of the invention.
Thus broadly, according to the invention, there is provided a method of treating a plant or crop which includes the step of exposing the plant or crop to an aqueous medium which contains treatment agents which include at least one wetting agent and calcium hypochlorite, the concentration of the calcium hypochlorite being between about 17.38 and 34.76 ppm.
The aqueous medium may be a treatment stream and exposing the plant or crop to the aqueous medium may include the steps of
generating an aqueous flow stream from a source of water;
introducing calcium hypochlorite into the aqueous flow stream to produce a treatment stream, the calcium hypochlorite producing hypochlorous acid, hypochlorite ions, calcium ions and hydroxyl ions when it is introduced into the aqueous flow stream, and the calcium hypochlorite being introduced into the flow stream so as to produce a treatment stream having a calcium hypochlorite concentration of between about 17.38 and 34.76 ppm and a calcium concentration of between about 7.6-15.2 ppm;
adding the or each wetting agent optionally to the water from which the flow stream is generated or to the flow stream or to the treatment stream; and
exposing the plant or crop to the treatment stream.
The calcium hypochlorite may be introduced into the aqueous flow stream so as to produce a treatment stream having a calcium hypochlorite concentration of between about 22.88 and 27.44 ppm and a calcium ion concentration of between about 10 and 12 ppm.
The method of the invention will typically be used for the treatment of growing crops. The plant or crop will thus typically be a growing crop. The crop may be selected from potatoes, stone fruit, apples, vines, onions, cucurbits such as pumpkins, melons and squashes, and leafy vegetables such as cabbage, lettuce, brussel sprouts and cauliflower or any crop which is prone to pathogenic or organism attack, including flowers.
The crop may thus be selected from potatoes, stone fruit, apples, vines, onions, cucurbits, leafy vegetables and flowers.
The calcium hypochlorite may be introduced into the aqueous flow stream by using an apparatus for controllably treating a liquid with a liquid treatment substance of the type described in the specification of U.S. Pat. No. 4,842,729.
The advantage of the use of an apparatus of the type described in U.S. Pat. No. 4,842,729 is that the time between contact of the water with the calcium hypochlorite, to form the required hydrolysis products and the time lag to contact the solution of hydrolysis products with the plant is so short that the beneficial ratio of hydrolysis products is retained. If calcium hypochlorite were merely mixed with water, this ionization ratio of hydrochlorous acid, hypochlorite ion and calcium hydroxide would fall into imbalance because of the instability and light sensitivity of hypochlorous acid, sedimentation of calcium hydroxide and because of side reaction of calcium hypochlorite with substances in the water stream. It is well documented that hypochlorous acid and hypochlorite form many defined and non-defined products with substances in water and the formation of these side reaction products is strictly time dependent. It is also well known that, to determine the chlorine demand of water, the tests are done over time periods from contact time to hours after contact time. The distance between the apparatus, e.g. the apparatus, and the sprays and the pressure of the water and the diameter of the conduit used are therefore selected to produce a short delay between formation of the solution and contact with the plant, as is described in further detail below.
The aqueous flow stream will typically be produced from municipal piped water or from irrigation water taken from a river, dam, borehole or the like.
The wetting agent, or surfactant, may be a silicone polyether wetting agent. It may, for example, be a silicone polyether copolymer and alcohol ethoxylate. These wetting agents are particularly suitable because they are not affected by the oxidizing properties of the treatment stream.
The aqueous medium may include about 0.005 to 0.05% and preferably about 0.01% of the wetting agent.
The method may thus include adding the wetting agent to the water from which the flow stream is generated or to the flow stream or to the treatment stream in an amount which is sufficient to produce a concentration of the wetting agent in the treatment stream of about 0.005-0.05% e.g preferably 0.01%. The wetting agent is necessary to enable the treatment stream to readily spread across the entire surface area of the plant which is being treated. The presence of a wetting agent, which allows the treatment stream to rapidly spread across the surface area of the plant so that the hypochlorous acid can rapidly exert its action before it dissipates, is an essential feature of the invention.
Exposing the plant or crop to the treatment stream may include the step of spraying the treatment stream onto the plant or crop with spraying means. The treatment stream may, for example, be sprayed onto the plant or crop via one or more spray nozzles.
The treatment substance may be introduced into the flow stream in an introduction zone of the flow stream.
The invention thus extends to a method of treating a plant or crop, the method including the steps of
generating an aqueous flow stream from a source of water;
introducing calcium hypochlorite into the aqueous flow stream to produce a treatment stream, the calcium hypochlorite producing a desired ratio of hypochlorous acid, hypochlorite ions, calcium ions and hydroxide ions when it is introduced into the aqueous flow stream, and the calcium hypochlorite being introduced into the aqueous flow stream so as to produce a treatment stream having a calcium hypochlorite concentration of between about 17.38 and 34.76 ppm and a calcium concentration of between about 7.6 and 15.2 ppm, the introduction of the calcium hypochlorite into the aqueous flow stream being done by means of an apparatus for controllably treating a liquid with a liquid treatment substance, the apparatus including
a body having a first portion providing a container-receiving zone and an opening leading into this zone, as well as a second portion having a liquid inlet and a liquid outlet defining a liquid flow path between them, with the zone being in communication with the liquid flow path;
a container for a liquid treatment substance, the container being located in the container-receiving zone and comprising a cylindrical sleeve, an end-piece closing off a first end of the cylindrical sleeve, at least one aperture in the sleeve in proximity to the first end, and seal means between the first end of the sleeve and the aperture, and being movable from an inoperative position in which the seal means seals fluid tightly against the first portion to prevent liquid passing from the flow path into the aperture, to an operative position in which the seal means permits controlled passage of liquid from the flow passage across the seal means into and out of the inside of the sleeve via the aperture in the sleeve, when the container is in its operative position;
at least one water treatment substance tablet comprising calcium hypochlorite as an active agent, inside the container;
bias means inside the body and biassing the first end of the sleeve away from the liquid flow path; and
actuating means for displacing the sleeve between the inoperative and operative postions;
adding at least one wetting agent to the flow stream or to the treatment stream; and
exposing the plant and crop to the treatment stream.
According to a further aspect of the invention, there is provided a treatment installation for the treatment of plants or crops, the installation including
calcium hypochlorite introduction means for introducing calcium hypochlorite into an aqueous flow stream to produce a treatment stream, the calcium hypochlorite producing hypochlorous acid, hypochlorite ions, calcium ions and hydroxyl ions when it is introduced into the aqueous flow stream,
an inlet conduit through which in use the aqueous flow stream flows to the calcium hypochlorite introduction means;
an outlet conduit through which in use the treatment stream flows from the calcium hypochlorite introduction means; and
outlet means connected to, and in flow communication with, the outlet conduit, for directing the treatment stream into a plant or crop.
The treatment installation may include wetting agent introduction means for introducing a wetting agent into one of the flow stream and the treatment stream. Instead, the aqueous flow stream may be produced from water and the installation may include wetting agent introduction means for introducing a wetting agent into the water.
The calcium hypochlorite introduction means may be an apparatus for controllably treating a liquid with a liquid treatment substance of the type described in the specification of U.S. Pat. No. 4,842,729.
The installation may include flow stream generating means for generating the aqueous flow stream. The generating means may be arranged to produce an aqueous flow stream having a pressure of between about 40-80 psi.
The flow stream generating means may be a pump.
The installation may include a non-return valve upstream of the introduction means and downstream of the flow stream generating means.
The outlet means may be in the form of at least one nozzle, spray head or the like, typically multiple nozzles in a preselected configuration. The or each nozzle, spray head or the like may be located at a distance of about 1-2 m from the calcium hypochlorite introduction means. The nozzles may be ALBUZ mister nozzles which produce a relatively large drop and operate at a generally lower pressure than most other nozzles.
The installation may further include filtering means for filtering the treatment stream.
The invention extends to crop-spraying equipment which includes an apparatus for controllably treating a liquid substance of the type described in the specification of U.S. Pat. No. 4,842,729.
The invention extends, further, to crop-spraying equipment which includes
an apparatus for controllably treating a liquid with a liquid treatment substance, the apparatus including
a body having a first portion providing a container-receiving zone and an opening leading into this zone, as well as a second portion having a liquid inlet and a liquid outlet defining a liquid flow path between them, with the zone being in communication with the liquid flow path;
a container for a liquid treatment substance, the container being located in the container-receiving zone and comprising a cylindrical sleeve, an end-piece closing off a first end of the cylindrical sleeve, at least one aperture in the sleeve in proximity to the first end, and seal means between the first end of the sleeve and the aperture, and being movable from an inoperative position in which the seal means seals fluid tightly against the first portion to prevent liquid passing from the flow path into the aperture, to an operative position in which the seal means permits passage of liquid from the flow passage across the seal means into and out of the inside of the sleeve via the aperture in the sleeve, when the container is in its operative position;
bias means inside the body and biassing the first end of the sleeve out of the liquid flow path;
actuating means for displacing the sleeve between the inoperative and operative positions;
an inlet conduit through which an aqueous flow stream can flow to the apparatus;
an outlet conduit through which the aqueous flow stream can flow from the apparatus; and
nozzle means, in flow communication with the outlet conduit, for spraying the aqueous stream onto a crop.
The liquid inlet may be aligned with the liquid outlet so that the liquid flow path is linear. The zone or chamber may be of elongate cylindrical form, and may extend orthogonally to the liquid flow path. It may be located between the liquid inlet and the liquid outlet.
The chamber and flow path may be circular in cross-section.
The bias means may comprise a spring located inside the body, between the liquid inlet and the liquid outlet and aligned with the chamber. The chamber as well as the chamber extension may have the same diameter.
The other or second end of the cylindrical sleeve of the container may also be closed off with an end-piece. The end-piece at the second end of the sleeve may be fixedly attached to the sleeve. The sleeve and end-pieces may be of plastics material, with the end-piece at the second end of the sleeve being integral with, e.g. welded to, the sleeve. The end-piece may have a larger diameter than the sleeve so that it protrudes radially outwardly from the sleeve. The sleeve may be provided with a plurality of the apertures in proximity to its first end, i.e. it may be foraminous or apertured in proximity to its first end. Its apertured portion may constitute less than half of the total length of the sleeve, and even less than one fifth its total length, e.g. about 5-10% of its length.
The seal means may comprise an O-ring of compressible material located in a circumferential groove in the sleeve. The O-ring may comprise an annular body portion as well as a circumferential lip-like portion extending radially outwardly from the body portion.
The apparatus may include calcium hypochlorite in the form of tablets located one above the other in the basket.
Typically, the ratio of the diameter of the container to its length may be between 1:2 and 1:4, e.g. about 1:3. The apertures may be spaced apart circumferentially, and may be generally square or rectangular, having bottom edges which extend parallel to the first end of the sleeve, i.e. orthogonally to its axis. The apertures may be arranged in a plurality of axially spaced rows, the apertures in one row being located equidistantly from the first end of the sleeve. The row of apertures located closest to the sleeve""s first end, may be positioned so that their bottom edges are spaced 0.5 to 2 cm from the base, e.g. about 1 cm. The width of the groove accommodating the seal ring may be between 2 and 5 mm, e.g. about 3 mm.
The actuating means may include a closure member closing off the chamber opening, the closure member comprising a circular cover portion and a peripheral skirt depending from the cover portion, with the skirt adapted to pass around that portion of the body providing the opening to the chamber. The actuating means may also comprise an external screw thread formation on the body around the opening, and a complemental internal screw thread formation on the closure member, the length of the basket being such that it protrudes from the open end of the chamber and abuts against the underside of the cover portion of the closure member.
The apparatus may include seal means located between the screw thread formation on the body portion providing the chamber opening and the free end of the chamber, and adapted to seal fluid tightly against the inner surface of the skirt of the closure member between the internal screw thread formation on the skirt and the cover portion of the closure member. The seal means may comprise a first O-ring of compressible or resilient material, e.g. rubber, located in a circumferential groove in the body, as well as a second O-ring located around the first O-ring within the groove. The second O-ring may be of less resilient material than the first O-ring, e.g. of TEFLON (tradename). In one embodiment, the second O-ring may comprise an annular body portion and a circumferential flange-like portion extending radially outwardly from the body portion. In another embodiment, it may comprise an annular body having a peripheral slit so that, on the chamber being pressurized, air will enter the slit thereby causing the ring body to flare open and seal effectively against the closure member.
Typically, the apparatus as described above will form part of tractor-drawn crop-spraying equipment. However, they can also form part of a hand-held spraying installation. Tractor drawn equipment typically comprises a water tank having a capacity of between about 500 and 2000 litres and a positive pressure pump which is driven from the power take-off of the tractor and which draws water from the tank and distributes it though spray nozzles. The nozzles may be of the type which operate at a pressure of about 60-80 psi and are particularly suitable for use with the apparatus as hereinbefore described. The nozzles will typically have different aperture sizes and will typically be arranged in suitable configurations depending upon the application. The crop-spraying equipment, as is consistent with most commercial equipment in use, typically includes a boom on which the nozzles are mounted. The boom may, for example, be a laterally extending boom so that several rows of crops can be sprayed simultaneously. Instead, it may be a vertical or diagonally arranged spray boom for spraying trees in orchards. Instead of a boom, the crop-spraying equipment may be fitted with vertically mounted sprays or lateral sprays for orchards and optionally with towers to spray an orchard from above. The crop-spraying equipment may, optionally, include an in-line filter to ensure that particles of calcium hypochlorite which may be dislodged from cartridges do not block the nozzle apertures of the crop spraying equipment.
Typically, the wetting agent will be introduced into the water in the tank and the apparatus will be installed between the pump and the spray nozzles or boom.
As it is important to the method of the invention that the crop or plant is fully exposed to the treatment stream, by using nozzles which produce relatively large drops which are carried effectively without substantial loss of hypochlorous acid and then rapidly dispersed on the surface of the plant by the wetting agent. The configuration of the boom and nozzles will be adjusted or selected to suit the requirements of a particular crop or plant so that effective wetting by the treatment stream is achieved.
The combination of calcium with the middle lamella galacturonic pectin structure of plants has long been recognised. Calcium aids the plant in its inherent ability to protect itself from attack by microorganisms by supporting the pectin structure and the physiology of cell metabolism of the outer cuticle. In a plant, calcium is well known and widely described in its function to maintain cell integrity by combining with pectins in what has been described as the xe2x80x9cegg boxxe2x80x9d effect, in which calcium is held in the spaces between two galacturonic acid chains by forming a coordination complex with the hydroxyl oxygens and the galacturonic acid carboxyl group. Because of recognition of the importance of calcium in protecting and fortifying the outer structure of plants, attempts have been made by horticulturists to artificially incorporate calcium into the cell wall structure, i.e. the spraying of plants and products with calcium chloride. These attempts have not met with success.
The Applicant believes that the combination of calcium ions and hydroxide ions in conjunction with hypochlorous acid and hypochlorite ions according to the invention enhances the ability of the plant to absorb and bind calcium ions into its middle lamella. This enhances the ability of the plant cell tissue to retain water and maintain its physiological processes. This is evident in FIG. 14 which shows the maintenance of foliage development under heat stress in potato trials using this epidermal fortification technique. Thereby the plant is enabled to sustain its normal biological functions and overcome attach by micro organisms. Furthermore, if there are lesions on the plant surface, the hypochlorous acid will, by its oxidising nature, immobilise enzymes excreted by the plant at the site of the lesion which in turn will, in the presence of the calcium ions enable the sealing off of the lesion and subsequently create a barrier to infection at the lesion.
Because of time dependent and unwanted side reactions of calcium hypochlorite with the flow stream the method may include adjusting the rate of flow of the flow stream, the rate of introduction of the calcium hypochlorite into the flow stream and locating the spraying means at a predetermined position downstream of the introduction zone so that the treatment stream, having a concentration of about 17.38-34.76 ppm calcium hypochlorite is sprayed onto the plant or crop very shortly after the treatment stream is produced, typically within about 0.29 and 13.4 seconds of production of the treatment stream. This ensures minimal side reactions of the calcium hypochlorite before the treatment solution comes into contact with the plant or crop and ensures that the hydrolysis ionization ratio between hypochlorous acid, hypochlorite ions and calcium hydroxide remains within the desired limits according to the requirements of the invention. For example, when the calcium hypochlorite is introduced into the flow stream by using the apparatus, the nozzles will generally be located at a distance of about 1-3 m downstream of the dispenser when the pressure of the flow stream is between about 40 and 80 psi using a pipe having a diameter of about 1.8 cm.
The method will typically be conducted using an aqueous flow stream having a pH of between about 6.8 and 7.4. This pH range is suitable because of the increase in pH by about 0.2-0.3 caused by the alkalinity of the calcium hydroxide produced when the water makes contact with the calcium hypochlorite. A lower pH also serves to limit the ionization of hypochlorous acid to hypochlorite.